Saules enerģijas izmantošana zemas temperatūras centralizētajā siltumapgādē

The district heating (DH) system`s infrastructure plays an important role to improve the energy efficiency and adapt available renewable energy sources (RES) to energy consumption. DH heating network connects buildings in different areas of cities and other settlements, so different centralized boiler houses or several smaller heat sources can supply the heat for consumers. This approach allows using any heat source integrated into the DH system. However, the heat consumption of buildings continues to decrease and it is often not economically viable to connect energy efficient buildings to a standard heat supply system. One of solutions is to use a heat carrier with a lower temperature that allows reducing heat losses and investments of the pipelines. In addition, RES can be used as a heat sources more efficiently.

The energy sector should implement different types of renewable energy technologies to increase the overall resilience against different unfavourable external conditions. The decision makers in the energy sector have a wide variety from which to choose the most suitable technology for energy production. Solar energy continues to increase its role in the energy sectors in most of the European countries due to lower environmental impact and decrease of technology costs.

The aim of the Thesis is to develop and test the methodology for evaluation of different solar energy integration strategies in low temperature DH systems. To achieve this goal, the following tasks have been set: perform the particular district heating system; to identify the long-term transformation paths for DH system; to evaluate solar energy potential and test various technical solutions and operation strategies for solar energy integration in DH; rank the analysed solar energy system configurations; determine the main aspects influencing the solar system performance. Several methods are combined within the research including regression analyses, system dynamic modelling, multi-criteria analyses and mathematical modelling.

The Thesis is based on the eight thematically unified scientific publications. Those publications are published in various scientific periodicals, and are accessible in scientific information repositories and cited international databases. The purpose of these publications is to highlight different technological solutions and aspects that need to be taken into account for sustainable development of solar DH systems.

This thesis consists of an introduction and three chapters.  The work introduction includes the objectives and tasks of the work, describes the structure of the work and gives a brief overview of the approbation of the doctoral thesis (publication, participation in international conferences and monographs). The second chapter of the work includes a methodology describing the developed methodology and solar system models, while the third chapter presents the results regarding identification of DH transformation path, three different technical solutions for solar system integration and comprehensive comparison of those alternatives. Finally, conclusions are given at the end of the Thesis.